A drill bit used to drill rocks and other materials, performs the operation of breaking rock and forming holes.
A drill bit according to conventional art is described below with reference to FIGS. 1A to 1D.
Referring to FIG. 1a, a rock drill bit 10 includes a drill bit head 30 and a skirt 50. The head of the rock drill bit 10 includes a plurality of rock crushing members in the form of buttons on a drill surface that comes into contact with rock. The rock is smashed and crushed by the members.
Referring to FIG. 1b, it can be seen that, in an array of drill bit buttons according to the conventional art, buttons 2 and 3 have the same radius r2 from the central axis C of the drill bit 10 and buttons 4 to 6 have the same radius r3.
When the plurality of buttons have the same radius extending from the central axis of the drill bit 10, the striking distribution is different to a certain extent according to the RPM (revolutions per minute) and the BPM (blows per minute).
Referring to FIG. 1c, it can be seen that the RPM and the BPM are set to appropriate values (a first condition) and thus relatively different points are struck. In contrast, under a specific RPM and BPM condition (a second condition) identical points may be struck. In this case, it can be seen that some buttons (a third group) strike the same point, as illustrated in FIG. 1d. 
Accordingly, the drill bit 10 that repeatedly strikes the same point under a specific condition is problematic in that rock crushing efficiency is low and the time it takes to crush rock is excessively long.
(Patent document 1) KR2007-0053285 A
(Patent document 2) KR2006-0110271 A